Studies Of Colloids Behavior And Effects In Porous Media

With the economic development and population increase, the shortage of water resource is increasingly serious in the coastal region. The excessive exploitation of groundwater leads to seawater intrusion. Nowadays, the main recovery method of seawater intrusion is artificial recharge. However, the disturbance effects of hydro geochemistry and hydrodynamic lead to a series of processes as colloids release, flocculation, transport and deposition on the sea-fresh water interface and air-water interface These processes can lead to the destruction of aquifer and the sudden change of permeability, which in turn can render restoration efforts ineffective. Adopting batch experiments, packed column experiment, microscope slide experiment, minisize glass column, taking the aquifers sample containing minim clay mineral (mainly illite) in Dagu River aquifer, this paper studies the series colloids behavior and it effect on permeability.(1) Using both batch and packed column experiment, we find the difference in critical solution concentration (CSC) and critical flocculation concentration (CFC). For NaCl solution, the critical solution. concentration and critical flocculation concentration are 60mmol/L and 40mmol/L; for seawater and freshwater mixed solution, the critical solution concentration and critical flocculation concentration are 6800μs/cm and 4800μs/cm. Colloids flocculation is an important factor for permeability decrease. (2) The result of abrupt salinity change experiments and gradual salinity change of experiments show that the permeability in the abrupt salinity change decreased by 60%, but in the gradual salinity change reduced only 50%. Abrupt changes in salinity can lead to a flush of particle release, which in turn then leads to pore clogging due to a jamming effect and then to a reduction of permeability. A gradual change in salinity, on the other hand, leads to a more gradual particle release and there is less chance for pore jamming. So flocculation and swelling is very important for permeability decrease in during gradual salinity change. (3)The permeability decreased more during constant head than during constant flux, Indeed, the total amount of particles flushed from the constant-flux column was 236 mg, but only 168 mg from the constant-head column. The flow regime for particle transport in all our experiments was dominated by advection. The particle Peclet numbers were large. Based on a regression equation relating the particle Peclet number to a dimensionless clogging parameter y. We can find that there was little hydrodynamic drag imposed on the flow by deposited particles, and that most drag was imposed by the collector.We use microscope slide and minisize glass column to study the colloids release on the air-water interface. The colloids release is visualized using confocal laser scanning microscopy and quantified by image analysis. The result show that there are many colloids released on the air-water interface. Most of colloids are release in the first interface movement. The hydrophobic colloids detached in larger amounts than did the hydrophilic colloids. For the hydrophilic colloids, detachment of the positively-charged colloids is significantly less than of the, negatively-charged colloids. For the hydrophobic colloids, no significant difference in detachment between positively-and negatively-charged colloids. Removal of colloids increase with decreasing velocity of the air-water interface. The positively-charged colloids were more sensitive to interface velocity than the negatively-charged colloids. However, Under this experiment condition (0.4-400cm/h), the relationship between detachment and velocity was not linear. Under advancing contact angle condition, the amount of released colloids is larger than under advancing contact angle condition, the difference of rate of detachment colloids can be up to 58.8%. When the salt concentration is high than critical solution concentration, the concentration on the air-water interface is similar. However, when the salt concentration is lower than critical solution concentration, the colloids concentration increase with the salt concentration decrease.